Nucleic acid-based methods for controlling gene expression have significantly impacted research involving gene pathways and function (Patil, et al., AAPS Jour, 7, E61 (2005), McManus, et al., Nat. Rev. Genet. 3, 737 (2002), Le-bedeva, et al., Annu. Rev. Pharmacol. Toxicol. 41, 403 (2001)). In addition, antisense therapies are potentially powerful candidates for clinical treatments of various ailments, including cancer, HIV/AIDS, and other diseases (Patil, et al., supra., Jason, et al., Toxic. And Appl. Pharm. 201, 66 (2004)). One antisense agent, Vitravene™, is currently used to treat retinitis in AIDS patents (Patil, et al., supra.). In conventional antisense approaches, oligonucleotides designed to hybridize with target mRNA sequences are delivered to a cell in a variety of ways. This hybridization leads to a down-regulation in the expression of the corresponding translated proteins. While the potential of antisense oligodeoxynucleotides (ASODNs) was recognized over twenty years ago (Stephenson, et al., Proc. Not. Acad. Sci. U.S.A. 75, 285 (1978) Zamecnik, et al., Proc. Nat. Acad. Sci. U.S.A. 75, 280 (1978)), their development into viable therapeutic systems has faced challenges with regard to stable transfection and entry into diverse cell types, toxicity, and low efficacy. To address these fundamental barriers, various transfection agents have been developed to shuttle nucleic acids into cells. These include cationic lipids and polymers, modified viruses, dendrimers, liposomes, and nanoparticles (Patil, et al., supra, Jason, et al., supra., Bharali et al., Proc. Nat. Acad. Sci. U.S.A. 102, 11539 (2005), Bielinska, et al., Bioconjugate Chem. 10, 843 (1999)). Along with developments in delivery platforms, efforts have focused on developing nucleic acid analogs and investigating their potential as ASODNs. These include ODNs having phosphorothioate- or morpholino-modified backbones and peptide nucleic acids (PNAs) (De Mesmaeker, et al., Acc. Chem. Res. 28, 366 (1995), Myers, et al., Org. Lett. 5, 2695 (2003)). In some cases, the modified ASODNs provide enhanced stability in the presence of cellular endo- and exonucleases and stronger binding affinity with complementary sequences. Most antisense experiments use modified ASODNs in combination with a delivery mechanism in order to achieve maximum efficacy. While many combinations of carriers and modified ASODNs show promise, no single system has emerged that is vastly superior to others. Typical methods such as using phosphorothioate ASODNs complexed with cationic lipid carriers are often only useful in serum-free transfectins and are semi-toxic to certain cell types, thus limiting their general utility and their potential in therapeutics.
Gold nanoparticles have proven to be extremely useful for diagnostic and other applications. Detailed studies of gold nanoparticles surface-functionalized with both nucleic acids and proteins demonstrate a number of unique and highly useful characteristics of such structures. For instance, oligonucleotides attached to gold nanoparticles bind more strongly and more specifically to complementary oligonucleotides than do oligonucleotides that are not attached to gold nanoparticles. These observations are, in general, associated with the surface density of the oligonucleotide on the nanoparticle (i.e., surface density). The change in hybridization of the oligonucleotide (bound to a nanoparticle) to a target polynucleotide is reflected in an increase in melting temperature (Tm), a sharper melting profile, and/or a decease in the dissociation constant (Kdiss) of the resulting hybridization complex compare to hybridization of the free oligonucleotide and the target polynucleotide. These binding events can furthermore alter the physical, electronic and optical properties of the gold nanoparticles in useful ways such as producing characteristic spectral shifts upon the specific binding of an attached oligonucleotide to its complement. Carbohydrates, lipids and proteins such as antibodies can also be attached to gold nanoparticles either individually or in combination.
To improve upon current methods, there exists a need in the art for an ideal antisense system that would feature high uptake efficiencies across many cell types, high intracellular stability, and a strong binding affinity to target mRNA, while maintaining a very low toxicity to either non-targeted cells when the application requires cell killing, or toward the targeted cells when gene manipulation is desired for other applications.